fix building by gcc45

WebDAV fixes:

*) check unsafe Destination
*) omit '\0' from "Location" header on MKCOL request

gzip related fixes:

*) do not disable gzip for MSIE 6.0 SV1 in "gzip_disable msie6"
*) nginx always sent "Vary: Accept-Encoding",
   if both gzip_static and gzip_vary were on

allow cross device temporary files atomic copying

various header fixes:

*) allow to proxy_pass_header/fastcgi_pass_header "X-Accel-Redirect",
   "X-Accel-Limit-Rate", "X-Accel-Buffering", and "X-Accel-Charset"
*) fix handling "Last-Modified" and "Accept-Ranges" for upstream responses
*) clear "Accept-Ranges" for SSI responses

fix variuos segfaults:

*) fix segfault if 400 or 414 errors are handled intricately
*) ngx_http_upstream_create() to cleanup the previous upstream after
   internal redirect

various image filter fixes and features:

*) variables support in image_filter
*) fix transparency in GIF
*) fix alpha-channel transparency in PNG
*) image_filter_transparency

various SSL fixes and features:

*) $ssl_client_verify
*) "ssl_verify_client ask" was changed to "ssl_verify_client optional"
*) ssl_crl
*) delete OpenSSL pre-0.9.7 compatibility: the sources were not actually
   compatible with OpenSSL 0.9.6 since ssl_session_cache introduction
*) fix memory corruption in $ssl_client_cert
*) issue SNI warning instead of failure: this is too common case
*) use ngx_log_error(), since OpenSSL does not set an error on the failure
*) add SNI support in -V output

geo module supports trusted proxies

ngx_http_geoip_module